Transmission system for an electric vehicle

ABSTRACT

A transmission system for an electric vehicle. The system includes a gearbox containing gears and a lubricating fluid. A pump is provided for supplying and removing lubricating fluid from the gear box. The operation of the pump is controlled by a controller. A reservoir is provided for storing lubricating fluid. The controller is configured to control the pump so that a portion of the lubricating fluid is removed from the gear box when the vehicle is involved in a high acceleration event.

The present disclosure related generally to the field of transmissionsystems for an electric vehicle. Specifically, a lubricated transmissionsystem for an electric vehicle.

In an electric car, efficient use of electrical power is extremelyimportant. There are various different components in a vehicle's drivetrain, and if any of these components are not operating efficiently thevehicle and its user may be deprived of range, time and power associatedwith use of the electric vehicle that may otherwise be available. Anelectric vehicle typically relies solely on stored electric power. Thus,there is a need to convert electric energy to propulsion power asefficiently as possible.

The present application discloses a transmission system for an electricvehicle that improves the efficiency of the power transfer within thetransmission system and, thus, provides for increased range, operatingtime and power for an electric vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects, and advantages of the present invention willbecome apparent from the following description, and the accompanyingexemplary embodiments shown in the drawings, which are briefly describedbelow.

FIG. 1 is a schematic block diagram of various components of anexemplary embodiment of a power train of an electric vehicle.

FIG. 2 is a schematic block diagram of various components of anexemplary embodiment of a power train of an electric vehicle.

FIG. 3 is a schematic block diagram of various components of atransmission system for an electric vehicle.

FIG. 4 is a schematic end view of two gears of a gear box coupled to adrive train in accordance with various disclosed embodiments.

DETAILED DESCRIPTION

As disclosed herein, a transmission system for an electric vehicle isprovided. The vehicle includes a DC power source to supply power to oneor more propulsion motors. The transmission may be used to change thespeed of the motor shaft to match the desired speed of the shaft drivinga wheel of the vehicle. The DC power source in an electric vehicle maybe the main battery of the electric vehicle.

FIG. 1 shows an exemplary electric vehicle 100 configured to be drivenby a pair of propulsion motors 172, 174. The vehicle may include arechargeable energy storage system 150 (e.g., a battery). The vehiclemay also include an engine 120 to provide supplemental power. The engine120 may generally refer to any apparatus operable to augment power orrange beyond the range associated with power provided by the battery150. For example, the engine 120 may be an internal combustion enginethat consumes gasoline. The storage system 150 may be, for example (butnot limited to) a high-voltage battery, such as a high-voltage lithiumion battery pack. Operation of the vehicle 100 may be driven by eachpower source and/or both. The vehicle 100 may include multipleelectrical motor/generators 172, 174 that may be operated either asdrive motors that convert electrical power to rotational mechanicalenergy or as generators that convert rotational mechanical energy toelectrical energy. The motor/generators are at times referred to simplyas motors but, as described herein, include the ability to be driven togenerate electricity. The motor/generators may be electrically drivenand coupled to the engine 120 and the storage device 150.

According to various embodiments, the vehicle 100 includes a firstmotor/generator 172 that serves as a motor to drive the front wheels 110of the vehicle. In the regenerative braking mode the motor 172 may serveas a generator to charge the storage device 150. The vehicle 100 furtherincludes a second motor/generator 174 (e.g., rear wheel drive (RWD)motor) that engages a drive shaft that turns one or more rear wheels110. One or more intermediate devices, such as a rear gearbox 144 and arear differential 134, may be provided between the secondmotor/generator 174 and the rear wheels 110. Similarly, the vehicle 100may include a front gearbox 142 and a front differential 132, locatedbetween the front motor/generator 172 and the front wheels 110.

The vehicle 100 may further includes a generator 124 that is driven bythe engine 120 and generates power for propulsion or for charging thebattery 150. As further described below, the gearboxes 142, 144 may besingle speed gearboxes or multi-speed gearboxes. The motor/generators172, 174, 124 and the battery 150 may be coupled to a common DC bus 155.In some embodiments, the generator 124 and motor/generators 172, 174 maybe AC devices and electric conversion devices such as inverters 162,164, 166 may be coupled between the motor generators and the DC bus 155.The vehicle 100 may be operated normally as a RWD vehicle, with thefront wheels only powered when needed for additional power or traction.

When the vehicle accelerates or increases energy consumption, speed ofthe drive motors increase to deliver more power or energy to the wheels110. The turning of the motors may be reversed to provide regenerativebraking, which provides the impression of down-shifting the vehicle 10.This also generates energy that may be stored in the battery 150.Accordingly, in some embodiments, the vehicle 100 may actuateregenerative braking to slow the vehicle 100 rather than causing brakepads (not shown) to slow the wheels when a braking actuator isactivated.

The increase in speed of the drive motors when the vehicle acceleratescauses a decrease in the efficiency of the operation of the gear box dueto the increase and temperature and pressure of the lubricating oil inthe gear box. The efficiency decreases due to, for example, churninglosses of the lubricating oil, friction losses of the rotatingcomponents, and the increase in temperature (i.e., heat dissipation).The disclosed system lowers oil level in a reservoir, and adds oil tothe gear box, during a transient event. For example, the disclosedsystem provides for a system to temporarily add extra oil into thegearbox system during a transient event (e.g. high acceleration event)to provide for increased operational efficiency of the gears, bearings,shafts located in the gear box. The overall volume of the lubricatingoil is distributed throughout the system components including thereservoir, gear box, pump and the connecting lines (e.g, pipes,conduits, etc.).

The disclosed innovative transmission system accomplishes this increasein efficiency (or, reduces the amount of decrease in deficiency) bytemporarily adding a portion of lubricating oil from a reservoir to thegear box in order to increase efficiency of the gear box during a highacceleration event. The size or volume of the portion of the lubricatingoil is relatively small and depends on the size of the variouscomponents of the transmission system including, for example, theoverall volume of oil located in the gear box. For example, the presentsystem preferably adds about 500 ml of lubricating oil from thereservoir toward the gear box when a high acceleration event isdetected. Alternatively, the amount of oil removed from the reservoirmay be between 400-600 ml or other suitable amount. The normal volume ofoil in the reservoir may be about 2.5 liters. Thus, during a transientsituation of high acceleration the disclosed system removesapproximately 20 percent of the volume of oil from the reservoir andpumped toward the gear box. Substantially all of the oil removed fromthe reservoir is added to the gear box. The added volume of oil mayrange from about 15 to 25 percent of the total volume of oil used duringstandard operating conditions depending on the size of the gear box,reservoir and oil system.

In another example, the normal volume of oil in the reservoir may be 2.3liters and the system may be configured to transfer 500 ml of oil to thesystem and gear box. Thus, the transferred quantity of oil isapproximately 22 percent of the system volume.

FIG. 2 discloses an alternative exemplary embodiment of a power trainfor an electric vehicle 200 configured to be driven by a pair ofpropulsion motors 272, 274. Although not shown in FIG. 2, the vehiclemay be an all-wheel drive (AWD) vehicle and include two or four motorsand the capability of driving all four wheels simultaneously. Thevehicle 200 shown in FIG. 2 operates in the same basic manner as thevehicle of FIG. 1 and may include the same variations and embodiments ofthe system and components described above.

The vehicle 200 may include a rechargeable energy storage system 200(e.g., a battery). The vehicle may also include an engine 220 to providesupplemental power. The engine 220 may generally refer to any apparatusoperable to augment power or range beyond the range associated withpower provided by the battery 250. For example, the engine 220 may be aninternal combustion engine that consumes gasoline. The storage system250 may be, for example (but not limited to) a high-voltage battery,such as a high-voltage lithium ion battery pack. Operation of thevehicle 200 may be driven by each power source and/or both. The vehicle200 may include multiple electrical motor/generators 272, 274 that maybe operated either as drive motors that convert electrical power torotational mechanical energy or as generators that convert rotationalmechanical energy to electrical energy. The motor/generators are attimes referred to simply as motors but, as described herein, include theability to be driven to generate electricity. The motor/generators maybe electrically driven and coupled to the engine 220 and the storagedevice 250.

According to various embodiments, the vehicle 200 includes a pair ofmotor/generators 272, 274 that serve to drive the front wheels 210 ofthe vehicle. In the regenerative braking mode the motors 272, 274 mayserve as a generators to charge the storage device 250. The vehicle 200may include a gearbox 240 located between the motor/generators 272, 274and the front wheels 210. The gearbox 240 may be configured to be asplit gear box (i.e., drive each wheel independently from separatemotors), or an integrated gear box that allows one of the two motors272, 274 to drive both wheels 210 together.

The vehicle 200 may further include a generator 224 that is driven bythe engine 220 and generates power for propulsion or for charging thebattery 250. As further described below, the gearbox 240 may be singlespeed gearboxes or multi-speed gearboxes. The motor/generators 272, 274,224 and the battery 250 may be coupled to a common DC bus 255. In someembodiments, the generator 224 and motor/generators 272, 274 may be ACdevices and electric conversion devices such as inverters 262, 264, 266may be coupled between the motor generators and the DC bus 255. Thevehicle 200 may be operated normally as a FWD vehicle.

FIG. 3 discloses an exemplary transmission system 300 to be used in anelectric vehicle, such as those vehicles described above. However, theinnovative transmission system disclosed herein is not limited to thoseexemplary embodiments of electric vehicles disclosed in the presentapplication.

The disclosed transmission system 300 includes an oil reservoir 350,which can be, for instance, a dedicated oil sump for the transmissionsystem or a sump shared with other systems that use the same lubricatingfluid. The system includes a pump 390 driven by a motor 392. The pump390 may be any suitable type such as centrifugal, positive displacement(e.g., screw type, piston type, etc.). A screw type pump is preferred.The motor 392 includes a controller 394 for controlling operation of themotor 392 and, thus, the pump 390 as well. The pump may operate to movethe lubricating fluid or oil either toward or away from the componentsto be lubricated. The system may include various valves (not shown) toprevent the flow of oil in an undesirable direction when the pump is notoperating.

The system may further include a heat exchanger 380 for cooling thelubricating fluid. The heat exchanger may include a cooling fluid 384carried through the heat exchanger to remove heat from the fluid or oil.The lubricating fluid is provided to the gear box 340, described furtherbelow.

The system 300 may include a controller 394 for the motor 392. Thecontroller 394 may be configured to send a receive data to other vehiclecomponents. For example, the controller 394 may be connected to thevehicle CAN bus 396 or other similar data carrying system. The CAN bus396 may carry information from various vehicle components and sensorssuch as an inertia measuring unit (e.g., an acceleration sensor in x, yand/or z directions), a vehicle speed sensor (e.g., a wheel speedsensor), a propulsion motor speed sensor, a steering angle sensor. TheCAN bus may carry information regarding the acceleration of the vehicleto the controller. Alternatively, the controller 394 may be configuredto determine the acceleration of the vehicle based on the informationreceived from one or more of the vehicle sensors mentioned above.

The controller 394 may be configured so that when the vehicleacceleration is determined to be greater than a predetermined value, thecontroller directs the motor 392 to drive the pump 390 to remove oilfrom the gear box 340. The first predetermined value may be in a rangeof 1.0 to 1.4 G. Preferably, a set point of 1.2 G is used for thepredetermined value. The pump 390 only operates to remove a relativelysmall amount of oil from the gear box for the amount of time that thevehicle acceleration is taking place. Once the vehicle acceleration hasreturned below a second predetermined value the pump operates to returnthe removed quantity of oil to the gear box from the reservoir 350. Thesecond predetermined value is preferably in the range of 3.5 to 6.5 G.The preferred value of the second predetermined value is 0.5 G. Thus,the lubrication of the components in the gear box is not jeopardized dueto the small volume of oil removed, the short time duration of reductionof volume of oil in the gearbox, and the relative high pressure of theoil remaining in the gear box during the high acceleration event.

FIG. 4 shows the internals of an exemplary gear box 240. In theexemplary embodiment, a propulsion motor (172, 174, 272, 274) includes adrive shaft 241 that drives a motor gear 242. Each motor gear 242 drivesa larger gear 243 that is connected to a smaller gear 246 that engages awheel gear 245 that is connected to drive shaft 244 for each of thewheels. The drive shaft may alternatively be connected to a differential(132, 134). In alternative embodiments, the gear box may container moregears depending on the use of the vehicle (e.g., grades encountered, topdesired speed, etc.). The split gear box shown in FIG. 4 is exemplaryonly. In alternative embodiments, the gear box may be cross-connectedinternally to allow one motor to drive both wheels.

As utilized herein, the terms “approximately,” “about,” “substantially”,and similar terms are intended to have a broad meaning in harmony withthe common and accepted usage by those of ordinary skill in the art towhich the subject matter of this disclosure pertains. It should beunderstood by those of skill in the art who review this disclosure thatthese terms are intended to allow a description of certain featuresdescribed and claimed without restricting the scope of these features tothe precise numerical ranges provided. Accordingly, these terms shouldbe interpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimedare considered to be within the scope of the invention as recited in theappended claims.

It should be noted that the term “exemplary” as used herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” “connected,” and the like as used herein mean thejoining of two members directly or indirectly to one another. Suchjoining may be stationary (e.g., permanent) or moveable (e.g., removableor releasable). Such joining may be achieved with the two members or thetwo members and any additional intermediate members being integrallyformed as a single unitary body with one another or with the two membersor the two members and any additional intermediate members beingattached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,”“above,” “below,” etc.) are merely used to describe the orientation ofvarious elements in the figures. It should be noted that the orientationof various elements may differ according to other exemplary embodiments,and that such variations are intended to be encompassed by the presentdisclosure.

It is important to note that the construction and arrangement of thetransmission system and electric vehicle shown in the various exemplaryembodiments is illustrative only. Although only a few embodiments havebeen described in detail in this disclosure, those skilled in the artwho review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Forexample, elements shown as integrally formed may be constructed ofmultiple parts or elements, the position of elements may be reversed orotherwise varied, and the nature or number of discrete elements orpositions may be altered or varied. The order or sequence of any processor method steps may be varied or re-sequenced according to alternativeembodiments. Other substitutions, modifications, changes and omissionsmay also be made in the design, operating conditions and arrangement ofthe various exemplary embodiments without departing from the scope ofthe present invention.

What is claimed is:
 1. A transmission system for an electric vehiclecomprising: a gearbox containing gears and a lubricating fluid; a pumpfor supplying and removing lubricating fluid from the gear box, whereinoperation of the pump is controlled by a controller; a reservoir forstoring lubricating fluid; wherein controller is configured to controlthe pump so that a portion of the lubricating fluid is transferred fromthe reservoir toward the gear box when the vehicle is involved in a highacceleration event.
 2. The transmission system of claim 1, wherein theportion of the lubricating fluid is less than 100 ml.
 3. Thetransmission system of claim 1, wherein the portion of the lubricatingfluid is about 50 ml.
 4. The transmission system of claim 1, furthercomprising a motor for driving the pump.
 5. The transmission system ofclaim 4, wherein the controller directly controls the operation of themotor to thereby control the operation of the pump.
 6. The transmissionsystem of claim 1, wherein the controller is connected to a vehicle datacommunication bus, and wherein the data communication bus carries dataconfirming the existence of the high acceleration event to thecontroller.
 7. The transmission system of claim 1, wherein thecontroller is connected to a vehicle data communication bus, and whereinthe data communication bus carries data regarding the condition of aplurality of vehicle components; and wherein the controller isconfigured to determine whether a the high acceleration event existsbased on the condition of at least one of the plurality of the vehiclecomponents.
 8. The system of claim 1, wherein the controller isconfigured to control the pump to transfer the lubricating fluid fromthe reservoir when the vehicle's acceleration exceeds a firstpredetermined set point.
 9. The system of claim 1, wherein the firstpredetermined set point is at least 1.2 G.
 10. The system of claim 8,wherein the controller is configured to control the pump to transfer thefluid into the reservoir after the high acceleration event when thevehicle's acceleration reduces to a value less than a secondpredetermined set point.
 11. The system of claim 10, wherein the secondpredetermined set point is less than or equal to 0.5 G.
 12. Atransmission system for an electric vehicle comprising: a gearboxcontaining gears and a lubricating fluid; a reservoir for storinglubricating fluid; a pump for moving lubricating fluid into and out ofthe reservoir, wherein operation of the pump is controlled by acontroller; wherein controller is configured to control the pump so thata portion of the lubricating fluid is transferred into or out of thereservoir based on the acceleration of the vehicle.
 13. The system ofclaim 12, wherein the lubricating fluid is transferred out of thereservoir toward the gear box when a value for the acceleration of thevehicle rises above a first predetermined set point.
 14. The system ofclaim 13, wherein the first predetermined set point is 1.2 G.
 15. Thesystem of claim 12, wherein the lubricating fluid is transferred intothe reservoir when a value for the acceleration of the vehicle decreasesbelow a second predetermined set point.
 16. The system of claim 15,wherein the second predetermined set point is 0.5 G.
 17. The system ofclaim 12, wherein the controller is connected to a vehicle datacommunication bus, and wherein the data communication bus carries dataregarding the condition of a plurality of vehicle components; andwherein the controller is configured to determine the acceleration ofthe vehicle based on the condition of at least one of the plurality ofthe vehicle components.
 18. A method of operating a transmission systemfor an electric vehicle, wherein the system includes a gearboxcontaining gears and a lubricating fluid and a pump for transferringfluid into and out of a reservoir that stores the lubricating fluid, themethod comprising the steps of: operating the pump so that thelubricating fluid is transferred into or out of the reservoir based onthe acceleration of the vehicle.
 19. The method of claim 18, wherein thelubricating fluid is transferred out of the reservoir toward the gearbox when a value for the acceleration of the vehicle rises above a firstpredetermined set point.
 20. The method of claim 18, wherein thelubricating fluid is transferred into the reservoir when a value for theacceleration of the vehicle decreases below a second predetermined setpoint.